Hitherto, an epoxy resin molding material has widely been used in the technique of sealing electronic components such as transistors and ICs. This is because epoxy resin has a good balance between electrical characteristics, moisture resistance, heat resistance, mechanical characteristics, adhesiveness to an inserted product, and others. In the case of using, in particular, both of o-cresol Novolak type epoxy resin and a Novolak type phenol curing agent, the balance between these performances is excellent; thus, the resin has become the major current of base resin for molding-material for sealing.
As electronic instruments have been becoming smaller, lighter, and higher in performances in recent years, the packaging density thereof has been becoming higher. About electronic component devices, the package thereof has been changing from conventional pin-insert type packaging to surface mounting type packaging. In the case of mounting a semiconductor device onto a wiring board, pins are inserted into the wiring board and then the pins are soldered from the rear surface of the wiring board in conventional pin-insert type packaging. As a result, the package is not exposed directly to high temperature. However, in surface mounting type packaging, the total amount of a semiconductor device is treated with a solder bath or by means of a reflow device or the like; therefore, the device is exposed directly to soldering temperature. As a result, in a case where the package absorbs moisture, the absorbed water expands abruptly when the package is subjected to soldering. Thus, exfoliation is generated in the bonding interface or the package is cracked. For this reason, there is caused a problem that the reliability of the package is declined at the time of the packaging.
As a measure for solving the problem, adopted may be a method of carrying out damp-proof wrapping of ICs, or drying ICs sufficiently before the ICs are mounted onto a wiring board, and then using the dried ICs, or some other method (see, for example, pp. 254-256 of “Packaging Technique of Surface Mounting Type LSI Package, and Improvement in the Reliability thereof” edited by the Semiconductor and Integrated Circuit Division, Hitachi Ltd., Applied Technique Publishing Corporation (Ohyo Gizyutsu Shuppan according to transliteration), Nov. 16, 1988). However, these methods require labor and time, so that costs also increase. A different measure is a method of increasing the content of a filler in an epoxy resin molding material for sealing. According to this method, water absorbed in a semiconductor device can be decreased; however, the method has a problem that the fluidability of the epoxy resin molding material for sealing is decreased largely. As a method for increasing the content of a filler without deteriorating the fluidability of an epoxy resin molding material for sealing, suggested is a method of optimizing the particle diameter distribution of a filler (see Japanese Patent Application Laid-Open No. 06-224328). If the fluidability of epoxy resin molding material for sealing is low, there is also caused a new problem that gold wire sweep, voids, pinholes, and others are generated (see, for example, pp. 172-176 of “Improvement in Reliability of Semiconductor Sealing Resin” edited by Technical Information Institute Co., Ltd., Technical Information Institute Co., Ltd., Jan. 31, 1990).
As described above, if the fluidability of epoxy resin molding material for sealing is low, a new problem is also caused; thus, the fluidability of epoxy resin molding material for sealing has been desired to be improved without lowering the curability thereof. However, the above-mentioned method of optimizing the particle diameter distribution of a filler does not make it possible to improve the fluidability of epoxy resin molding material for sealing sufficiently.
An object of the invention is to provide an epoxy resin molding material for sealing that is excellent in fluidability and solder reflow resistance without lowering the curability thereof, and an electronic component device provided with an element sealed with the material.